Tgt

UniProt ID: Q9VPY8
Organism: Drosophila melanogaster
Review Status: COMPLETE
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Gene Description

Tgt (CG4947) encodes the Drosophila ortholog of QTRT1, the catalytic subunit of eukaryotic tRNA-guanine transglycosylase. Together with the accessory subunit CG3434 (QTRT2 ortholog) it exchanges guanine 34 at the anticodon wobble position of tRNA-Asp, tRNA-Asn, tRNA-His and tRNA-Tyr for queuine, a micronutrient base that animals obtain from diet and gut microbes, producing queuosine. The zinc-containing enzyme works by a double-displacement mechanism through a covalent enzyme-tRNA intermediate. Queuosine at the wobble position tunes decoding of NAC/NAU codons. Function in flies is inferred from orthologs; no Drosophila-specific experimental studies of the gene have been reported.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0002099 tRNA wobble guanine modification
IEA
GO_REF:0000120 		ACCEPT
Summary: tRNA wobble guanine modification (queuosine formation at G34).
Reason: The catalytic TGT subunit replaces G34 with queuine; this is the core process.
Supporting Evidence:
file:DROME/Tgt/Tgt-uniprot.txt
Reaction=guanosine(34) in tRNA + queuine = queuosine(34) in tRNA +
GO:0002099 tRNA wobble guanine modification
ISS
GO_REF:0000024 		ACCEPT
Summary: tRNA wobble guanine modification (queuosine formation at G34).
Reason: The catalytic TGT subunit replaces G34 with queuine; this is the core process.
Supporting Evidence:
file:DROME/Tgt/Tgt-uniprot.txt
Reaction=guanosine(34) in tRNA + queuine = queuosine(34) in tRNA +
GO:0005737 cytoplasm
IEA
GO_REF:0000120 		ACCEPT
Summary: Cytoplasm.
Reason: Eukaryotic TGT acts on cytoplasmic tRNAs; consistent with UniRule and orthologs.
Supporting Evidence:
file:DROME/Tgt/Tgt-uniprot.txt
SUBCELLULAR LOCATION: Cytoplasm
GO:0006400 tRNA modification
IEA
GO_REF:0000002 		MODIFY
Summary: Generic tRNA modification.
Reason: Correct but an uninformative parent; MODIFY to tRNA wobble guanine modification (queuosine formation at G34), which Tgt already carries (IEA, ISS).
Proposed replacements: tRNA wobble guanine modification
GO:0008479 tRNA-guanosine(34) queuine transglycosylase activity
IBA
GO_REF:0000033 		ACCEPT
Summary: tRNA-guanosine(34) queuine transglycosylase activity.
Reason: Tgt is the single fly member of the QTRT1 catalytic subfamily (PTHR43530:SF1) and carries the catalytic TGT domain; the activity is supported by phylogeny, similarity and rule.
Supporting Evidence:
file:DROME/Tgt/Tgt-uniprot.txt
Catalytic subunit of the queuine tRNA-ribosyltransferase
file:DROME/Tgt/Tgt-deep-research-falcon.md
human and mouse studies establish the detailed chemistry of the corresponding catalytic enzyme
GO:0008479 tRNA-guanosine(34) queuine transglycosylase activity
IEA
GO_REF:0000120 		ACCEPT
Summary: tRNA-guanosine(34) queuine transglycosylase activity.
Reason: Tgt is the single fly member of the QTRT1 catalytic subfamily (PTHR43530:SF1) and carries the catalytic TGT domain; the activity is supported by phylogeny, similarity and rule.
Supporting Evidence:
file:DROME/Tgt/Tgt-uniprot.txt
Catalytic subunit of the queuine tRNA-ribosyltransferase
file:DROME/Tgt/Tgt-deep-research-falcon.md
human and mouse studies establish the detailed chemistry of the corresponding catalytic enzyme
GO:0008479 tRNA-guanosine(34) queuine transglycosylase activity
ISS
GO_REF:0000024 		ACCEPT
Summary: tRNA-guanosine(34) queuine transglycosylase activity.
Reason: Tgt is the single fly member of the QTRT1 catalytic subfamily (PTHR43530:SF1) and carries the catalytic TGT domain; the activity is supported by phylogeny, similarity and rule.
Supporting Evidence:
file:DROME/Tgt/Tgt-uniprot.txt
Catalytic subunit of the queuine tRNA-ribosyltransferase
file:DROME/Tgt/Tgt-deep-research-falcon.md
human and mouse studies establish the detailed chemistry of the corresponding catalytic enzyme
GO:0032473 cytoplasmic side of mitochondrial outer membrane
ISS
GO_REF:0000024 		KEEP AS NON CORE
Summary: Cytoplasmic side of mitochondrial outer membrane, by similarity to mouse QTRT1.
Reason: Reported for mammalian QTRT1 but not examined in flies; cytoplasm is the established site of activity.
GO:0120507 tRNA-guanine transglycosylase complex
ISS
GO_REF:0000024 		ACCEPT
Summary: tRNA-guanine transglycosylase complex.
Reason: Eukaryotic TGT is a QTRT1-QTRT2 heterodimer; flies have single orthologs of both (Tgt and CG3434).
Supporting Evidence:
file:DROME/Tgt/Tgt-uniprot.txt
Heterodimer of a catalytic subunit and an accessory subunit.

Core Functions

Catalytic subunit of the Tgt-CG3434 tRNA-guanine transglycosylase that exchanges guanine 34 of GUN-anticodon tRNAs for salvaged queuine, forming queuosine.

Molecular Function:
tRNA-guanosine(34) queuine transglycosylase activity
Directly Involved In:
tRNA wobble guanine modification
Cellular Locations:
cytoplasm
In Complex:
tRNA-guanine transglycosylase complex
Supporting Evidence:
  • file:DROME/Tgt/Tgt-uniprot.txt
    Catalytic subunit of the queuine tRNA-ribosyltransferase
  • file:DROME/Tgt/Tgt-deep-research-falcon.md
    human and mouse studies establish the detailed chemistry of the corresponding catalytic enzyme

References

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Suggested Questions for Experts

Q: Is Tgt required for queuosine in Drosophila tRNAs, and does dietary or microbial queuine availability alter fly translation or physiology through Tgt?

Suggested Experiments

Experiment: Measure Q-tRNA by APB-northern or LC-MS in Tgt mutants raised on queuine-supplemented and queuine-free axenic diets.

Hypothesis: Tgt is the sole source of queuosine in fly tRNAs.

Deep Research

Falcon

(Tgt-deep-research-falcon.md)

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📚 Additional Documentation

Notes

(Tgt-notes.md)

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📄 View Raw YAML

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